ProShow Gold 4.52 is rather old, and I don't have it installed on my computer anymore, so I can't give you precise instructions. For that I would need to see the menus, and I can't.

So, here are some general instructions, based on the menus of Producer 4.5:In Slide Options, select the video layer and go to Layer Settings (or perhaps there is something called "Video Settings". Look for "Video Sound Settings". In volume, instead of the default 100% write 0.This will mute the sound of your video clip.

Still in Slide Options, go to Sound and then "Select Sound" > Select Sound FileThis will open the directories of your computer, and you can choose the audio file that you want to insert. Double click on that file to insert it in your slide.Now, if you look in your Slide List, notice that the slide has a sound icon on it, which is in addition to the soundtrack of your show.

If you want to fully synchronize between the beginning of the video and that of the sound that you attach, you can play with the offset values (from previous slide). These values can be positive or negative (put a minus in front of the number).